LAS VEGAS (AP) - Conor McGregor tapped out in the fourth round of his comeback fight at UFC 229 against Khabib Nurmagomedov, who then climbed over the cage and set off a brawl by scuffling with another fighter in McGregor's corner on Saturday night.

The wild scene occurred after McGregor (21-4) got caught in a choke by Nurmagomedov (27-0), who defended his lightweight belt with an impressive victory over the superstar who infamously attacked a bus carrying Nurmagomedov in Brooklyn last April.

But the Russian champion from Dagestan then exacerbated several months of hostilities between the fighters' camps. Nurmagomedov stepped away from the prone McGregor and immediately pointed at the Irishman's corner, shouting and throwing his mouthpiece.

The men in McGregor's corner appeared to respond with taunts, and Nurmagomedov climbed over the fence and fought with Dillon Danis, a Bellator welterweight who trains with McGregor. Meanwhile, two men apparently from Nurmagomedov's entourage entered the cage and sucker-punched McGregor, who defended himself before security personnel separated everyone.

Nurmagomedov and McGregor both left the ring before the championship belt could be put around Nurmagomedov's waist, and fans in the pro-Conor crowd threw beers and debris at Nurmagomedov on his way out. UFC President Dana White said he feared a melee in an arena if he awarded the belt to Nurmagomedov.

Both fighters' purses will be withheld pending an investigation by the Nevada Athletic Commission, White said. He also claimed three members of Nurmagomedov's entourage "are on their way to jail right now."

"I don't even know what to say right now," White said. "I'm just disgusted and sick over it. ... We had so much security and (police) here. I didn't see that one coming."

UFC heavyweight champion Daniel Cormier is a teammate of Nurmagomedov at their gym in San Jose, California. He attempted to calm Nurmagomedov after the bout.

"Two wrongs don't make it right," Cormier tweeted after the brawl. "Conor didn't deserve that. No one did. But some things aren't for fight promotion. Religion, family, country. Throwing stuff in Brooklyn. For Khabib it wasn't fight promotion, it was really personal. Diff culture man."

Nurmagomedov and McGregor made no secret of their mutual loathing in the past few months, and the UFC used footage of McGregor's attack on the bus to promote UFC 229, which could be the best-selling pay-per-view card in UFC history. McGregor lobbed several creative insults at Nurmagomedov during the promotion of this matchup, including labeling Nurmagomedov's manager, Ali Abdelaziz, as a "snitch terrorist rat."

The main event has been eagerly anticipated across the sport ever since McGregor threw a hand truck at a bus containing Nurmagomedov before a UFC show in Brooklyn last spring. McGregor was furious about a confrontation between Nurmagomedov and a member of McGregor's team earlier in the week.

McGregor was arrested after seriously hurting two other fighters with broken glass from the attack, but Nurmagomedov shrugged it off and won the lightweight title by beating Al Iaquinta. When McGregor agreed to return to the UFC, he eagerly accepted Nurmagomedov as his opponent.

Before the post-fight madness, Nurmagomedov firmly asserted his grappling dominance over McGregor's striking skill in the Irish superstar's first MMA bout in 23 months. McGregor hadn't been in a fight since losing his boxing match with Floyd Mayweather last year, and Nurmagomedov proved an insurmountably tough opponent for his comeback.

McGregor's dislike for Nurmagomedov likely fueled his decision to take a fight that created a difficult stylistic matchup for him. McGregor's strength is his striking, while Nurmagomedov is one of the most dominant grapplers in UFC history.

Four security guards separated the fighters while they didn't touch gloves before the bout, and Nurmagomedov went for a takedown in the opening minute while dominating the opening round.

Nurmagomedov staggered McGregor with a right hand early in the second round, but McGregor got up and landed a flying knee. Nurmagomedov made another takedown and steadily improved his position throughout a dominant round, eventually standing and raining down blows on the prone McGregor.

Nurmagomedov decided to stand and strike with McGregor in the third round, apparently unafraid of McGregor's famed power. McGregor landed several significant shots, but Nurmagomedov took them and eventually reasserted control against the cage.

McGregor did decent work in the fourth round before Nurmagomedov got control, climbed on McGregor's back and finally submitted the former two-division champion.

All three judges' scorecards favored Nurmagomedov 29-27, with the champion winning the second round 10-8 on all three cards. McGregor won the third round on every card.